1. Field of the Invention
The present invention relates to an electromagnetic clutch for a compressor used, for example, in an air conditioning apparatus for an automobile.
2. Description of the Related Art
In an air conditioning system for an automobile, a compressor is located in a refrigeration cycle of a refrigerating medium for a compression of the liquid flowing from an evaporator. An electromagnetic clutch is provided for a selective transmission of a rotational movement from a crankshaft of the internal combustion engine to the compressor, the clutch having a rotor rotatably supported at the housing of the compressor. The rotor has a frictional surface which faces, with a small spacing therebetween, a frictional surface of an armature supported by a hub via a holder and spring member, the hub being connected to a drive shaft of the compressor. The refrigeration medium in the compressor includes oil therein, for lubrication purposes, and although an oil seal is provided between the housing and the drive shaft of the compressor, small amount of leakage is inevitable via the oil seal, and the leaked oil, attached to the surface of the housing by its own viscosity, is sometimes transmitted to the frictional surface, if nothing is provided to prevent such a transmission of the leaked oil, and this causes a slippage between the frictional surfaces to occur. Therefore, to prevent such a transmission of leaked oil to the frictional surfaces, Japanese Unexamined Patent Publication No. 63-112630 has disclosed a concept whereby a ring-shaped shield is provided for discharging the leaked oil to the outside of the clutch.
In this prior art, an annular plate cover is connected to the armature on the side thereof opposite the frictional surface thereof, and a ring-shaped shield is connected to an inner peripheral wall of the rotor at a position adjacent to the inner race of the ball bearing, which rotatably supports the rotor on the boss portion of the housing, so that the ring shield extends axially and thus is radially outwardly covered by the annular plate. This arrangement makes its possible for the leaked oil to be diverted by the ring shield, caught by the cover, and exhausted to the outside, without being directed to the frictional surfaces. Nevertheless, under a particular situation caused, for example, by a dimensional limitation of the compressor and/or the clutch, it is sometimes impossible for a seal ring to be mounted in the way proposed by the above prior art disclosed in Japanese Unexamined Patent Publication No. 63-112630, and therefore, it has heretofore been necessary to provide a means for attaining the above-mentioned exhausting of leaked oil even when such a situation arises.